The invention relates to audio amplifiers and in particular to monolithic integrated circuit (IC) audio amplifiers useful in adaptive noise processor systems. Reference is made to a paper by James E. Solomon titled "THE MONOLITHIC OP AMP: A TUTORIAL STUDY" published in the IEEE Journal of Solid-State Circuits Volume SC-9 No. 6 for September, 1974 on pages 314-332. Also, reference is made to my U.S. Pat. No. 4,205,276 which is coauthored with William H. Gross and assigned to the assignee of the present invention. These references deal in detail with some of the elements useful in practicing the present invention. Reference is also made to a paper by Dr. Sergio Franco titled "Use Transconductance Amplifiers" in Electronic Design for Sept. 13, 1976, starting on page 98. This paper describes programmable active filter circuits.
In adaptive audio noise processors it has been found useful to provide a control amplifier that has a wide dynamic range, high linearity, and a frequency response that can be voltage controlled. Basically, the frequency response is used to mask out noise as a function of the audio signal content. Thus, audio noise is effectively processed so as to have a reduced perception to the listener.
It has been found that typical control amplifiers commonly produce an output that is related to its control action and not just the character of the audio content. This undesirable effect can be due to an offset response that is correctable in accordance with the invention.